1. Field
This disclosure relates to a control system for treadmill exercise machines with a fixed tread base and a moving tread belt upon which a user runs or walks. The disclosed device detects the position and time of user footfalls on the tread belt and adjusts tread belt speed to maintain the user's position relative to the fixed tread base.
2. Prior Art
Individuals commonly use treadmill exercise machines incorporating a moving belt over a tread base as a means of exercise similar to walking or running, but in a fixed location. Many users dislike using treadmill exercise machines, however. One reason is that they must manually set an exercise pace and then match that pace in order to stay safely centered on the tread base. This means of control is dissimilar to normal walking or running which allows the user to adjust speed semi-consciously in response to physical and mental state.
Several types of systems have been disclosed which measure the position of the user and automatically maintain the user's position on the tread base. These designs involve a variety of sensing means and control mechanisms. Despite these disclosures, the greatest majority of treadmill exercise machines do not incorporate automatically adjusted tread belt speed controls. The prior art has been commercially unsuccessful due to performance limitations and excessive production costs.
U.S. Pat. No. 4,708,337 issued to Shyu describes a treadmill speed control based on user body position sensing, preferably with an ultrasonic sensor, and incremental speed changes. However, accurate sensing of actual user position is complicated by the nature of human walking and running motion. Specifically, all portions of the user's body will be in relative motion with respect to the user's center of mass. This relative motion will vary from user to user and from one stride to the next for a single user. The result will be an unpredictable error in the user position control value of the disclosed systems. Control signal error is a principle limiter of performance in feedback control systems, often leading to instability. Additionally, incremental speed adjustments based on position zones or trigger lines result in slow, imprecise responses to user speed changes.
U.S. Pat. No. 5,314,391 issued to Potash describes infrared foot position sensors and also describes a proportional-integral control algorithm, based on a position control variable. The specification includes no detail of the foot sensors or a means of using them to determine user position. However, in-so-far as they protrude above the tread belt level, they may be perceived as non-aesthetic, they may be subject to obstruction by dirt or other objects, and they may be subject to damage due to their exposed position. The proportional-integral control system will be comparatively slow to respond to user speed changes because it employs user position relative to the tread base as the only feedback control variable. User position will only change gradually when the user changes speed. Control signal delay is a principle limiter of performance in feedback control systems.
U.S. Pat. No. 5,368,532 issued to Farnet describes an automatic treadmill speed control system incorporating two under-belt pressure sensors. Speed control is based on the sequence of sensor activations which can produce a positive, a negative, or a zero acceleration of the belt. The fixed acceleration rates of this system are common in the prior art. However, fixed acceleration rates are a crude form of control which severely limits the responsiveness of belt speed to changes in user motion. Further, the control algorithm is subject to many forms of error based on variation in user stride styles, user exercise rates, and user size. Pressure sensors may also be expensive and subject to excessive wear.
A system for automatic control of tread belt speed based on the position of the user has been disclosed in U.S. Pat. No. 5,800,314 issued to Sakakibara. The system described incorporates similar control and sensing features to earlier disclosures and shares their weaknesses. The system also provides a manual control allowing the user to change control system parameters. However, the system supports manual user selection from only two possible configurations via a mode setting switch. A manual selection may be inconvenient or confusing to the user. Further, two configurations may not allow for optimum control system performance in all modes of use. Finally, manual selection of control system parameters may not be a practical means to optimally set parameters for all operating conditions.
U.S. Pat. No. 6,135,924 issued to Gibbs discloses an automatic treadmill speed control similar to earlier systems but introducing an optical position sensor and calibration system. This new sensor type will suffer from the same unpredictable sensing errors as other whole-body sensing methods, and thus will not provide an acceptable performance.
A device for sensing the position of the user's feet on a jogging machine stepping board is disclosed in U.S. Pat. No. 7,094,180-B2 issued to Huang. However, the large number of sensors required to achieve reasonably accurate measurements limit economic viability, reliability, and performance of the disclosed system. The disclosure does not describe any specific sensor technology, mechanism for translation of sensor signals to speed control, or explanation for the edge placement of sensors. However, the edge placement of sensors increases the total number of sensors required and limits sensor accuracy.
The system disclosed in U.S. Pat. No. 7,094,180-B2 additionally claims to determine the speed of the user by measuring the width and time of a jogger pace between the contact positions and lift positions of two feet. However, the method disclosed will measure the average speed of the belt rather than the intended speed of the jogger. Thus the disclosed system will not provide an acceptable performance.
U.S. Pat. No. 7,101,319 issued to Potts discloses a three sensor under-belt foot sensing control systems to address problems of two sensor systems. However, the system described is still a fixed acceleration rate, zone-based system which will respond slowly and imprecisely to changes in user speed. It will also still suffer from performance variations due to variations in user size and user stride style.
U.S. Pat. Nos. 6,126,575, 6,179,754-B1, and 7,153,241-B2, issued to Wang, describe a range of linear above-belt non-touch sensor arrangements to detect foot position for the purpose of tread belt speed control. The disclosures describe no means to convert individual user foot detections for tread belt speed control. Specifically, the disclosures make no mention of the behavior of the disclosed system as a user's foot moves backward upon the tread belt and while no other footfall has yet been made upon the tread belt. Also, the disclosure includes no description of system performance while no user foot is in contact with the belt, as when running. These omissions limit the ability of one skilled in the art to use the disclosed devices in practical applications.
U.S. patent application Ser. No. 11/989,729 describes a treadmill speed control system incorporating forward and rearward mounted strain gauges. The disclosed system uses relative mechanical strain at these locations to estimate user position on the tread base. Resulting values will vary unpredictably based on user running style due to torques from user impact with the tread deck. Moreover, the system describes no means to estimate user position as the user's feet impact upon, translate upon, and leave the running surface during the course of a running or walking stride. Further, the disclosed sensors may be expensive and subject to excessive wear.
Within the prior art, no means are described to distinguish between an intentional foot placement versus an inadvertent or near foot placement on the tread belt. This might occur when the user drags a foot on or just above the belt while striding. The dragged foot may be detected by the various sensors described and consequently be used to control belt speed. Such erroneous reading will result in large and unpredictable error signals which will disrupt the operation of any speed control system.
The prior art also lacks any means to determine foot position more precisely than the spacing of foot sensors. This shortcoming reduces system performance for any sensor arrangement, or alternately, increases system cost for any desired performance level.